amx 69 brake system choice?

 Just a couple of thoughts... if you decide to use the OE Bendix four piston system, it's always wise to follow the procedures in the TSM. It can become pretty tedious when using shims to get the proper adjustment.
 Also, if you are planning to replace the brake lines, M/C and wheel cylinders, you may want to consider replacing with DOT 5 fluid. Lots of good info from previous discussions here on that topic. Do Forum search; brake fluid or DOT 5.
 When all done correctly, those OE brakes should still be able to stop a battleship.  Bruce

Red Devil wrote: In road tests of the day, the AMX actually stopped quite well. For general street cruising and shows, stock should be fine if well maintained and you drive within limits and fit good tires. The later Bendix sliding calipers are also not without issue as the steel-on-steel siding surfaces need good maintenance to work well - especially if you drive much on salted, winter roads (expect not a problem for you).  Porterfield still offers their R4S pads if wanting something with better fade resistance for the 4-piston Bendix, but I believe they are now custom order so around $210 a set. And there's always the Wilwood, Aerospace or Scarebird options as Frank mentioned.  Hope this helps, RD

The disks on my 70 work great and I have no plans on changing them. In fact I've driven it enough around Des Moines traffic that I've had to "test them" more than once and I can stop that puppy pretty well all things considered. I've just not had a problem. For prolonged braking heat may build and they may fade but I've not had major problems that way so far (and I've owned the car since about 2005)

The sliding calipers, any sliding calipers, either on the bracket or on the pins and bolts - all have issues unless maintained. The type like used on 81 Eagle slid on pins and if that finish went bad the caliper could stick. Same for ANY sliding caliper - drive it in Iowa, water, salt, sand, dust and dirt, lack of maintenance, and you see one side of the rotor cut to the fins and the other like new because the caliper failed to slide. 
I can't tell you how many IHP cars, Iowa Highway Patrol, I replaced rotors and calipers on. I've seen one side cut clean into the pad's BACKING and the rotor eaten to the fins while the other side was ok - yup, caliper failed to slide. 
Don't dismiss the multi-piston design. It worked.
Now as far as "clamping pressure" keep in mind it's PSI - force, pressure per square inch, so you must take into account the master cylinder bore size, the pressure applied there, then that "PSI" translated to the surface area of the backs of the pistons to get clamping forces. Can't simply say "more or less clamping force" without doing some serious math. 
If the Kelsey Hayes calipers like I put on my 73 hung up for any reason, and i've seen them hang, too - RUST on the big bolts they slide on gets flaky and stuck in the rubber, yeah, even they can fail to slide.

Since the rotors, pads, and calipers are available again for the stock 1968-70 brakes, I also recommend going back to stock. Despite the solid rotors, the stock disc setup works really well.

I prefer fixed calipers over sliding calipers. What everyone hated about multi piston calipers is one of the pistons would become stiffer than the rest and get stuck. Completely flushing the brake fluid any time the brakes are bled, or every 5 years is enough to prevent this problem.